1. Field of the Invention
My invention relates generally to traffic management of communications networks, and more specifically, Internet Protocol (IP) over reconfigurable WDM (Wavelength Division Multiplexing) optical networks. More particularly, my invention relates to methods and apparatus for performing dynamic reconfiguration migration of these networks from a current topology to a new topology.
2. Description of the Background
It appears that an important component of the next generation Internet will be IP over wavelength division multiplexing optical fiber networks (i.e., IP/WDM). WDM, a parallel transmission technology using sliced non-overlapping wavebands (i.e. wavelength channels) within a fiber, is used to explore the bandwidth of existing fiber networks. Each WDM channel provides high bandwidth, operates asynchronously and in parallel, and can operate at different rates and carry different data formats. IP is a main driver in today's successful Internet and provides a common traffic convergence layer for all types of applications. The convergence of these two technologies can provide many advantages.
One of the emerging IP/WDM architectures is IP over reconfigurable WDM (hereinafter referred to as IRW networks). Reconfigurable WDM networks comprise optical WDM add/drop multiplexers (OADM) and optical wavelength cross-connects (OXC) interconnected, for example, by an optical fiber mesh network. Communications through these networks are conducted over bi-directional circuit-switched connections consisting of wavelength lightpaths. Because of the circuit-switched capability, these WDM networks are highly reconfigurable. Traditionally, IP networks have been comprised of routers and fixed physical links statically interconnecting the interfaces of these routers. In this context, reconfigurable WDM networks acted as high bandwidth transport networks providing point to point interconnection between geographically disperse IP networks. In IRW networks, the IP and WDM technologies are converged and the WDM network acts as the core of the IP network providing the interconnection between the routers. In other words, a WDM network supports a virtual IP network, the router interfaces now being interconnected by circuit-switched lightpaths.
By converging these two technologies, IRW networks consist of two layers: the IP layer and the WDM layer. There are several models on how these two layers can be physically combined in the IRW architecture. The overlay model is one such model and an exemplary overlay network is shown in FIG. 1. This network comprises IP routers 110 and a reconfigurable WDM network 112, consisting of OXCs and wavelength add-drop multiplexers (WADMs) 115 interconnected by optical fibers 116. IP routers 110 are physically connected to WADMs 115 through physical links 118. A virtual IP network 120 comprises virtual connections 122 (shown by the dashed lines) interconnecting the IP routers 110, which virtual connections are formed through circuit-switched lightpaths established in the physical WDM network 112. In this arrangement, the WDM layer behaves like a server network to the IP layer. Management and control of the two layers remain separate, with well-defined interaction interfaces between them. A further description of this technology can be found in, IETF Internet draft, “IP Over Optical Networks: A Framework”, by Rajagopalan et. al. (this latter document can be obtained from the IETF).
An advantage of IRW networks is that the resulting virtual IP topology is reconfigurable because the circuit-switched lightpaths of the physical WDM network are reconfigurable. In other words, the same physical WDM fiber topology can support a number of lightpath topologies and therefore a number of virtual IP topologies. As result, IP traffic engineering can be performed through traditional management mechanisms, used for fixed IP topologies, and also through dynamic adaptation/reconfiguration. In addition, because of the nature of the WDM network, reconfiguration can be performed while the network is operating and transporting end user traffic.
Of concern here is this ability to perform dynamic reconfiguration, and in particular, how to dynamically migrate the current virtual IP topology to a new topology while minimizing the effect on the end user. As is further described below, an IRW traffic engineering system comprises reconfiguration triggers, which are policies that determine when a network reconfiguration should be performed, and topology design algorithms, which determine new virtual IP network topologies given specific objective functions and traffic distributions. However, once a new virtual IP topology is determined, the physical network must be reconfigured/migrated to realize that topology. Reconfiguration migration comprises establishing and taking down individual lightpath connections and reconfiguring the IP routers in a particular sequence such that the old network topology is removed and the new network topology is realized. Because the WDM network, IP connections, and IP router interfaces are being physically modified, dynamic topology migration significantly affects the end user traffic. Hence, migration schemes are needed to minimize this impact.
In general, IP virtual topology networks and the traffic engineering of these networks are not new; in particular, ATM networks are used to transport IP. However, these networks are viewed as static networks. In other words, migrating a virtual network topology means completely breaking down the network system, interrupting service, configuring the new network, and then re-establishing service. As a result, topology reconfiguration in static overlay networks, like IP over classical ATM, is rarely performed.